1. Technical Field
The present invention relates to a sequence allocation method and a sequence allocating apparatus for allocating a Zadoff-Chu sequence or GCL sequence to a cell.
2. Description of the Related Art
Mobile communication systems represented by a cellular communication system or wireless radio LAN (i.e., local area network) systems are provided with a random access region in their transmission regions. This random access region is provided in an uplink transmission region when a terminal station (hereinafter, “UE”) sends a connection request to a base station (hereinafter, “BS”) for the first time, or when a UE makes a new band allocation request in a centralized control system where a BS or the like allocates transmission times and transmission bands to UEs. The base station may be referred to as an “access point” or “Node B.”
Furthermore, in a system using TDMA (i.e., time division multiple access) such as the 3GPP RAN LTE, which is currently undergoing standardization, when a connection request is made for the first time (which takes place not only when a UE is powered on but also when uplink transmission timing synchronization is not established such as when handover is in progress, when communication is not carried out for a certain period of time, and when synchronization is lost due to channel conditions, and so on), random access is used for a first process of acquiring uplink transmission timing synchronization, connection request to a BS (i.e., association request) or band allocation request (i.e., resource request).
A random access burst (hereinafter, “RA burst”) transmitted in a random access region (hereinafter, “RA slot”), unlike other scheduled channels, results in reception errors and retransmission due to collision between signature sequences (situation in which a plurality of UEs transmit the same signature sequence using the same RA slot) or interference between signature sequences. Collision of RA bursts or the occurrence of reception errors increases processing delays in the acquisition of uplink transmission timing synchronization including RA bursts and processing of association request to the BS. For this reason, a reduction of the collision rate of signature sequences and improvement of detection characteristics of signature sequences are required.
As the method for improving the detection characteristics of signature sequences, generation of a signature sequence from a GCL (i.e., generalized chirp like) sequence having a low auto-correlation characteristic and also a low inter-sequence cross-correlation characteristic or Zadoff-Chu sequence is understudy. A signal sequence, constituting a random access channel and known between transmitter and receiver, is referred to as a “preamble” and a preamble is generally comprised of a signal sequence having better auto-correlation and cross-correlation characteristics. Furthermore, a signature is one preamble pattern, and suppose the signature sequence and preamble pattern are synonymous here.
Non-Patent Documents 1 to 3 use a Zadoff-Chu sequence or GCL sequence, whose sequence length N is a prime number, as an RA burst preamble. Here, adopting a prime number for sequence length N makes it possible to use N−1 sequences with optimal auto-correlation characteristics and cross-correlation characteristics, and optimizes (makes a correlation amplitude value √N constant) cross-correlation characteristics between any two sequences of the available sequences. Therefore, the system can allocate any sequence out of the available Zadoff-Chu sequences to each cell as a preamble.
Non-Patent Document 1: R1-062174, Panasonic, NTT DoCoMo “Random access sequence comparison for E-UTRA”
Non-Patent Document 2: R1-061816, Huawei, “Expanded sets of ZCZ-GCL random access preamble”
Non-Patent Document 3: R1-062066, Motorola, “Preamble Sequence Design for Non-Synchronized Random Access”